1. Field of the Invention
The present invention relates to electromagnetic field measuring apparatus having an electromagnetic field measuring sensor, and a method therefor, for measuring an electromagnetic field developed by an electromagnetic noise radiated from an electronic device.
2. Description of the Related Art
Up to now, an electromagnetic field measuring sensor is adapted to measure an electromagnetic field that exists in the extreme vicinity of a conductor surface of an electronic device in a countermeasure against an electromagnetic interference (EMI) of the electronic device that radiates an electromagnetic noise. The electromagnetic field measuring sensor measures an electric field and a magnetic field at respective positions on the conductor surface, and obtains an electric field distribution and a magnetic field distribution over the entire conductor surface, thereby visualizing a location of a noise radiation source. In general, the noise radiation source is a location that functions as a wave source, a propagation path, and an antenna, and the location is specified to perform the efficiency of a countermeasure against the noise.
FIG. 10 illustrates an electromagnetic field component in a printed circuit board 1 of an electronic device. A vertical component is dominant in an electric field of the printed circuit board 1, and can be represented by Ez (V/m). The electric field component Ez is measured, thereby enabling a radiation source being a high impedance to be detected. Also, a horizontal component is dominant in a magnetic field of the printed circuit board 1, and can be represented by two components Hx and Hy (A/m) orthogonal to each other. Those two magnetic field components Hx and Hy are measured, thereby enabling a radiation source of a low impedance to be detected. That is, the radiation source in the printed circuit board 1 is required to measure those three components Ez, Hx, and Hy (three components of the electromagnetic field).
Up to now, those three components Ez, Hx, and Hy of the electromagnetic field are measured by sensors corresponding to the respective components. As an electric field sensor, a monopole antenna sensor has been generally known. The electric field component Ez in the vertical direction can be measured by the monopole antenna sensor. Also, as a magnetic field sensor, a loop antenna sensor has been known. A magnetic field component Hx (or Hy) in a direction perpendicular to a loop can be measured by the loop antenna sensor. The remaining magnetic field component Hy (or Hx) is measured by rotating the loop antenna sensor about a direction perpendicular to the printed circuit board 1 as an axis by 90 degrees. That is, it is general that the measurement of the electric field by the monopole antenna sensor and the measurement of the magnetic field by the loop antenna sensor are conducted, individually.
On the contrary, U.S. Pat. No. 6,456,070 discloses an electromagnetic field sensor that measures an electric field and a magnetic field at the same time. An electromagnetic field sensor 10 disclosed in U.S. Pat No. 6,456,070 is illustrated in FIG. 11. Referring to FIG. 11, reference numeral 12 and 13 denotes coaxial cables arranged in parallel to each other, which are connected to contact connectors 14 and 15, respectively. Ends of the coaxial cables 12 and 13 at sides opposite to the contact connectors 14 and 15 are connected to each other through a loop antenna 11 which is formed of an inner conductor of a coaxial cable. Current values that flow in the coaxial cables 12 and 13 are detected, respectively, and the detected values are calculated, thereby separating a current generated by the electric field and a current generated by the magnetic field from each other. With the above operation, two components of the electric field component Ez and the magnetic field component Hx (or Hy) are measured at the same time.
Also, the remaining magnetic field component Hy (or Hx) is measured by rotating the loop antenna sensor 11 about a direction perpendicular to the printed circuit board 1 as an axis by 90 degrees.
In recent years, with higher function of the electronic device, the radiation electromagnetic noises that mainly cause EMI have been changed from steady and cyclic noises to noises that temporally change. The noises that temporally change are directed to noises that change according to the operating state of a device such as a movable part or a data communication device. The change in the noises leads to a change of the electromagnetic field to be measured from a steady and cyclic electromagnetic field to an electromagnetic field that temporally fluctuates. That is, in order to observe a relationship between the electric field and the magnetic field which temporally change in synchronism with the operating state, the intensity of a current, the direction of the current, and so on, there is a need to measure three components of the electromagnetic field by an electromagnetic field measuring sensor at the same time.
However, the electromagnetic field sensor disclosed in U.S. Pat. No. 6,456,070 cannot measure two components Hx and Hy of the magnetic field at the same time. Accordingly, the electromagnetic field is caused to change while the electromagnetic field sensor is rotating by 90 degrees with the result that an appearance of the electromagnetic field that temporally fluctuates cannot be observed.